This application is based on Japanese Patent Application No. 2002-202902 filed on Jul. 11, 2002, the disclosure of which is incorporated herein by reference.
The present invention relates to physical quantity detection equipment for detecting physical quantity.
Recently, a physical quantity sensor for detecting a physical quantity such as pressure, temperature, and acceleration, is much required in accordance with the home automation and the car automation. When a physical quantity sensor having a single measurement range is set to detect a large change in physical quantity, the sensor cannot detect a fine change in the physical quantity. In this case, detection resolution of the sensor, i.e., detection accuracy, is comparatively low. Conversely, when the sensor is set to have high detection accuracy, the sensor cannot detect a large change in the physical quantity.
To detect both a large and fine change in physical quantity, a physical quantity sensor having a plurality of measurement ranges is proposed. As shown in FIG. 8, a physical quantity sensor 50 includes three sensing units 50a-50c. Each sensing unit 50a-50c has a sensing device 51a-51c, an amplifier 52a-52c, and an output circuit 55a-55c. Each output circuit 55a-55c connects to an electronic control unit (i.e., ECU) 30 through a wire harness, respectively.
Here, by providing each amplifier 52a-52c a different offset, for example, the amplifier 52a in the sensing unit 51a operates as a linear amplifier in the first measurement range between P0 and P1, as shown in FIG. 9. Similarly, the amplifier 52b operates in the second measurement range between P1 and P2, and the amplifier 52c operates in the third measurement range between P2 and P3. Accordingly, the sensor 50 can detect a pressure change in a wide pressure range by switching a plurality of sensing units 50a-50c having a different offset.
However, the sensor 50 according to a related art necessitates a plurality of sensing units 50a-50c, so that both cost and size of the sensor 50 increase.
In view of the above problems, it is an object of the present invention to provide physical quantity detection equipment having only one sensing unit for detecting both a large and a fine change in physical quantity. It is another object of the present invention to provide a detecting method for detecting both a large and a fine change in physical quantity
Physical quantity detection equipment includes a detector, an amplifier, an offset adjustment device, an addition device, and an output device. The detector detects physical quantity and outputs a first voltage corresponding to the detected physical quantity. The amplifier amplifies the first voltage. The offset adjustment device determines a measurement range of the amplified first voltage among a plurality of predetermined measurement ranges, and outputs a second voltage corresponding to the determined measurement range. The addition device subtracts the second voltage from the amplified first voltage, and outputs the subtracted amplified first voltage, which is in the determined voltage range. The output device outputs the subtracted amplified first voltage to an outside circuit, and informs the determined measurement range to the outside circuit. The outside circuit calculates the physical quantity based on the subtracted amplified first voltage and the determined measurement range.
A variable range of the subtracted amplified first voltage can be set comparatively large, so that the outside circuit detects the subtracted amplified first voltage accurately. Therefore, the equipment can detect the physical quantity in a wide range without decreasing the detection accuracy substantially. Thus, the equipment detects both a large and a fine change in the physical quantity.
Preferably, the output device controls consumption current, which is current consumed in the output device and is supplied to the output device from the outside circuit. The controlled consumption current corresponds to the determined measurement range so that the output device informs the determined measurement range to the outside circuit.
Preferably, the output device supplies current to the outside circuit. Here, the supplied current corresponds to the determined measurement range so that the output means informs the determined measurement range to the outside circuit.
Preferably, the output device modulates the subtracted amplified first voltage with a predetermined frequency corresponding to the determined measurement range, and outputs the modulated subtracted amplified first voltage to the outside circuit so that the output device informs both the subtracted amplified first voltage and the determined measurement range to the outside circuit.
Preferably, the output device includes a first circuit for outputting the subtracted amplified output voltage to the outside circuit and a second circuit for outputting a range signal corresponding to the determined measurement range to the outside circuit.
Next, a method for detecting physical quantity includes the steps of detecting physical quantity, so that a first voltage corresponding to the detected physical quantity is outputted, determining a measurement range of the first voltage among a plurality of predetermined measurement ranges, so that a second voltage corresponding to the determined measurement range is outputted, subtracting the second voltage from the first voltage, and outputting the subtracted first voltage and an information about the determined measurement range.
A variable range of the subtracted first voltage can be set comparatively large, so that the subtracted first voltage is detected accurately. Therefore, the physical quantity can be detected in a wide range without decreasing the detection accuracy substantially. Thus, both a large and a fine change in the physical quantity can be detected.
Preferably, the subtracted first voltage and the information about the determined measurement range are detected by an outside circuit so that the outside circuit calculates the physical quantity based on the subtracted first voltage and the information about the determined measurement range.
Preferably, the outputting step further includes the step of controlling consumption current, which is consumed in a circuit that provides the outputting step and is supplied from an outside circuit. Here the consumption current corresponds to the determined measurement range so that the outside circuit calculates the physical quantity based on the subtracted first voltage and the determined measurement range.
Preferably, the outputting step further includes the step of supplying current to an outside circuit. Here the current corresponds to the determined measurement range so that the outside circuit calculates the physical quantity based on the subtracted first voltage and the determined measurement range.
Preferably, the outputting step further includes the steps of modulating the subtracted first voltage with a predetermined frequency corresponding to the determined measurement range, and outputting the modulated subtracted first voltage to an outside circuit so that the outside circuit calculates the physical quantity based on the modulated subtracted first voltage.